Empty or inaccessible files ion shared folder in WindowsXP guest

Description

I've had this issue with WindowsXP guest on a Windows7 host using VirtualBox versions from 4.1.14 to 4.2.4.
The issue is: Files on a shared folder mounted in WinXP seem to be corrupted or empty when opened by windows programs unless I open them once in a DOS command box (example: dos command type). After that, the files become accessible also from within Windows programs like Word or Wordpad.
A downgrade to 4.0.16 fixed the problem. Now the files are accesible and intact from the v ery beginning no matter if I use DOS or windows programs.